function externalLinks() {  
 if (!document.getElementsByTagName) return;  
 var anchors = document.getElementsByTagName("a"); 
 for (var i=0; i< anchors.length; i++) {
 	
   var anchor = anchors[i];
   if  (anchor.getAttribute('href') &&
   		anchor.getAttribute('rel') == 'external')
		anchor.target = '_blank';
 }  
}  
window.onload = externalLinks;